Macedonian President Boris Trajkovski is feared dead after a plane taking him to an international conference crashed in Bosnia-Hercegovina.
Trajkovski became Macedonian president in 1999
The plane, with eight others on board, came down in rain and fog in mountains near the town of Stolac.
Nato peacekeepers and emergency workers spent the day searching for wreckage.
The BBC's Nick Hawton in Sarajevo describes Mr Trajkovski as a key figure who helped broker a peace deal with ethnic Albanian rebels in 2001.
Hours after the crash, Nato peacekeepers said they were still hunting for the wreckage and that no bodies had been recovered. Authorities said they still considered the plane to be officially "missing".
"The area is mountainous and heavily mined with few roads and
when you couple this with weather and the size of the search area it
makes the operation incredibly challenging and difficult," said Nato spokesman Dave Sullivan.
Earlier, Bosnian officials said wreckage and bodies had been found, but the reports were later denied.
In Macedonia, officials said parliament speaker Ljubco Jordanovski would
serve as acting president.
Security has been tightened along the country's borders and at key state and army institutions.
A spokesman for US peacekeepers in Bosnia said the plane lost contact with air-traffic controllers near the border between Bosnia and Montenegro.
The plane took off from the Macedonian capital, Skopje, earlier on Thursday.
The plane vanished in poor weather. Picture: Igor Bozinovski
Mr Trajkovski and a group of advisers were on their way to an investment conference in Mostar.
It was near Stolac, east of the Croatian port of Dubrovnik, when it vanished.
The nine people on board included seven conference delegates and two pilots. The delegates were believed to include senior advisers to the president.
International tributes were paid as news of the disappearance spread.
Javier Solana, the European Union's foreign and security affairs
chief, called it "a very tragic day for Macedonia, for all
the people of that country but also for many people in
"President Trajkovski was a great man, a man of passion,
a man who moved his country forward, not only the reforms
but also to get it as close as possible to Europe," Mr Solana
said in a statement.
Irish Prime Minister Bertie Ahern, whose country holds the
EU's rotating presidency, described Mr Trajkovski as having
"contributed hugely to reconciliation in Macedonia" and
as a strong supporter of Macedonia's ambition to become an
Only on Wednesday he signed Macedonia's formal application to join the EU, which was due to be submitted to the EU's Irish presidency in Dublin on Thursday.
That event has now been postponed.